The goal of this project is to relate the biochemical and mechanical states of the mechanism of muscle contraction by studying the detailed mechanical properties of muscle preparations in which the concentration of relevant chemical species is subject to experimental variation. Force transients, which occur after the length or load on the muscle is rapidly altered and are related to molecular events of the crossbridge cycle, will be measured in conditions of reduced myofibrillar concentration of the reaction substrate (ATP), at increased concentration of the reaction products (ADP and Pi) and at altered pH. These conditions can be imposed on "skinned" muscle preparatins which have had the surface membrane removed. The effects of the altered chemical on the transient events will be related of the known kinetics of actomyosin in solution to determine how organization of the filament lattice influences rates of the intermediate reactions and how free energy change of the chemical reaction is coupled into force generation. A new light diffraction method, using acousto-optic deflection, is to be developed to record and control sarcomere length at the high spacial and time resolution necessary to perform the transient experiment in skinned muscle fibers.